Sinead O'Connor has said she is cancelling her 2012 tour due to her bipolar disorder.

The singer made the announcement in a posting on her website, saying that she is "very unwell" and had been advised by her doctor not to hit the road after her "very serious breakdown between December and March".

In December, Sinead announced her split from therapist Barry Herridge after 16 days of marriage, although she has since tweeted about them getting back together "for, like, ever".

The Irish singer-songwriter is best known for the early 1990s hit Nothing Compares 2 U.

Her latest album - How About I Be Me (And You Be You)? - was released in February.

The 45-year-old says she had planned the tour because of the album's release, but was "attempting to be stronger than I actually am".